The present invention relates generally to control valves and flow regulating valves, and more particularly to valves that will handle molten polymer flow at elevated pressures and temperatures.
Controlling molten polymer shut off and flow rates under extreme conditions of temperature and pressure is problematic. These extreme conditions normally include pressures up to and including 2000 psig at temperatures up to and including 300xc2x0 C. Such pressures and temperatures are often used in experimenting with new polymers in a polymerization reactor under laboratory conditions. Under these conditions pressure control and flow control is often achieved by precise regulation of flows of molten polymer to or from the reactors. Known valves such as the Demi(trademark) valve (G+D15 series manufactured by G.W. Dahl Company, Inc of Bristol, RI. 02809) have a maximum operating pressure of 750 psig at temperatures of 230xc2x0 C. The large actuator of the Demi(trademark) valve, which must be kept cool, makes compact installations of heated valves very difficult and cumbersome. Thus, a valve that operates at both high temperature and pressure, is compact and easily kept heated is desirable. Such a valve is also believed desirable for more general uses at lower less extreme temperatures and pressures where it is expected to function well and its compact size and simple construction is of value.
The following disclosures may be relevant to various aspects of the present invention and may be briefly summarized as follows:
U.S. Pat. No. 4,794,940 to Albert et al describes a diaphragm valve having two elastomeric diaphragms with a piston therebetween. The body is made of plastic, metal or other materials and comprises a valve base, a spacer ring and a cap. A first diaphragm is clamped between the bottom of the spacer ring and the valve base and a second diaphragm is clamped between the top of the spacer ring and the cap. The spacer ring has a double diameter bore containing a double diameter piston that is contacting both diaphragms. The diaphragm material can be conventional flexible materials such as Teflon, rubber, silicone rubber, or other material impervious to gas or liquid flowing through the valve. One preferred embodiment is a fabric reinforced elastomer 0.06 inches thick. Such a valve cannot handle extreme high temperatures and pressures.
U.S. Pat. No. 3,897,041 to Cowan describes a fluid logic valve that controls xe2x80x9chigh pressurexe2x80x9d air (80 psi). The valve uses two elastomeric diaphragms with a double diameter control element therebetween and functions in much the same manner as the Albert reference xe2x80x2940. It is indicated that flow through the valve may either be quickly stopped by snap action or the valve can be used in an analog fashion to partly restrict flow. The diaphragm is a thin flexible elastomeric member. Such a valve cannot handle extreme high temperatures and pressures.
It is desirable to have a valve at the reactor exit to control polymer flow and the valve must be able to be used at the same temperature and pressure as the polymer in the reactor. The high temperatures and high pressures impose high forces on the valve elements that must reliably operate without binding or seizing. It is desired to place the valve in the same hot bath as the reactor; therefore, the valve must be remotely actuated. It is also desirable to have a valve of compact size to accommodate the small size of the baths normally used in laboratory environments. It is also desired that the actuator not have to be kept cool as this is a source of heat loss from the reactors.
Briefly stated and in accordance with one aspect of the present invention, there is provided a compact fluid actuated diaphragm valve comprising: a bottom valve body portion having conduits for process fluid in fluid communication with a bottom diaphragm cavity, the bottom diaphragm cavity having a bottom end surface in fluid communication with a first process fluid conduit and a valve seat centered in the bottom diaphragm cavity and protruding from the bottom end surface, the valve seat being in fluid communication with a second process fluid conduit that terminates in an orifice centered in the valve seat, the bottom diaphragm cavity having a bottom shoulder that supports an edge portion of a metallic process diaphragm having a first side spaced from the valve seat and capable of deflection to contact the valve seat, the bottom shoulder having a bottom annular recess contacting the edge portion of the process diaphragm; a process side seal contacting the edge portion of the process diaphragm; an annular sleeve closely fitting in the bottom diaphragm cavity, having a first sleeve end and a second sleeve end, the first sleeve end bearing against the process seal for holding the process seal and process diaphragm in place against the bottom shoulder, the sleeve having a bore centered over the valve seat; a cylindrical diaphragm actuating button, having a major cylindrical button diameter, slidably fitting in the bore of the sleeve and having a first button end surface contacting a second side of the process diaphragm opposite the valve seat, and having a second button end surface, opposed to the first button end surface, the distance between the first button end surfaced and second button end surface defining a button length; a top valve body member having a control fluid conduit for a control fluid in fluid communication with a control diaphragm cavity, the control diaphragm cavity having a top end surface in fluid communication with the control fluid conduit and a stop surface centered in the control diaphragm cavity and protruding from the top end surface, the control diaphragm cavity having a top shoulder that supports an edge portion of a metallic control diaphragm spaced from the stop surface and capable of deflection to contact the stop surface, the control diaphragm cavity of the top valve body member closely fitting around the annular sleeve; a control side seal contacting the edge portion of the control diaphragm; a top annular recess at an interface between the top shoulder and the sleeve, the recess accommodating the edge portion of the control diaphragm and the control seal, the top shoulder and the second sleeve end cooperating so the control seal and edge portion of the control diaphragm are held in the top recess against the top shoulder, the stop surface centered over the bore in the sleeve, the control diaphragm and process diaphragm containing the actuating button therebetween; and fastener means extending from the top valve body member to the bottom valve body member, the fastener means exerting a force forming a process seal at the edge portion of the process diaphragm and a control seal at the edge portion of the control diaphragm, the fastening between the top valve body member and the bottom valve body member creating an assembled valve cavity distance between the valve seat and the stop surface, the valve cavity distance being greater than the button length by about the sum of the distances that each diaphragm is capable of deflecting in the assembly.